Question

When I leave the app and come back to it’s ‘on’ sate sometimes it works fine by turning the torch/flash on but most of the time it either flashes or remains off.

AppDeligate.m

- (id) init {
torchState = TRUE;
if( (self=[super init] )) {
    /// initialize flashlight
    // test if this class even exists to ensure flashlight is turned on ONLY for iOS 4 and above
    Class captureDeviceClass = NSClassFromString(@"AVCaptureDevice");
    if (captureDeviceClass != nil) {

        AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

        if ([device hasTorch] && [device hasFlash]){

            if (device.torchMode == AVCaptureTorchModeOff) {

                NSLog(@"Setting up flashlight for later use...");

                AVCaptureDeviceInput *flashInput = [AVCaptureDeviceInput deviceInputWithDevice:device error: nil];
                AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];

                AVCaptureSession *session = [[AVCaptureSession alloc] init];

                [session beginConfiguration];
                [device lockForConfiguration:nil];

                [session addInput:flashInput];
                [session addOutput:output];

                [device unlockForConfiguration];

                [output release];

                [session commitConfiguration];
                [session startRunning];

                [self setTorchSession:session];
                [session release];
            }

        }

    } 
} 
return self;
}

- (void)toggleTorch {
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    [device lockForConfiguration:nil];
    // For the first 4 to 5 times comming back from multiask this first if hits and works properly

    if (torchState == TRUE && device.torchMode == AVCaptureTorchModeOff) {
        NSLog(@"AVCaptureTorchModeOff setting On");
        // On the 4th or 5th time it flashes and stays off or does nothing staying OFF
        // even though the NSLog fires

        [device setTorchMode:AVCaptureTorchModeOn];
        [device setFlashMode:AVCaptureFlashModeOn];

    } else if (torchState == TRUE && device.torchMode == AVCaptureTorchModeOn) {
        // Sometimes this randomly fires and every time ErrorNotification fires too
        NSLog(@"AVCaptureTorchModeOn");
        if (AVCaptureSessionRuntimeErrorNotification) {
            NSLog(@"ERROR"); 
            // Try to force but doesn't do anything
            [device setTorchMode:AVCaptureTorchModeOn];
            [device setFlashMode:AVCaptureFlashModeOn];
        }    
    } else {
        NSLog(@"ALL IS OFF");
        // when torch is in the off state it returns off as it should
        torchState = FALSE;
        [device setTorchMode:AVCaptureTorchModeOff];
        [device setFlashMode:AVCaptureFlashModeOff];
    }
    [device unlockForConfiguration];
}

-(void) applicationDidEnterForeground:(UIApplication*)application {
    [self toggleTorch];
}

The only thing I haven’t included in code is a touch even that calls toggleTorch for on/off. That piece works great so again, what I’m testing here is turning it on at launch aka DidEnterForeground as well as when the app is returned to from a multitask session.

Answer 1

I would change 2 things:
1. add it to ApplicationDidBecomeActive
2. don’t use toggle torch but set the state you want it to be (so you won’t turn it off twice or on twice…). So change the function to toggleTorchWithState…

That what I’ve done in one of my apps and that works perfectly.